1. Field of the Invention
This invention relates to a digital video tape recorder for recording and reproducing digital video signals.
2. Description of Related Art
With the progress in the digital recording system, a digital VTR (DVTR) capable of recording/reproducing pictures with a picture quality higher than that achievable with the analog VTR employing a low carrier wave FM recording system, is being put to practical application.
Although not shown, the constitution of the recording/reproducing system for the digital VTR is schematically explained hereinbelow.
In the recording system, input analog video signals are converted by an analog/digital (A/D) converter into digital signals which are segmented into blocks each being of a suitable size. The resulting block-based signals are compressed and encoded for error correction and error concealment on the block basis. In the reproducing system, synchronizing signals are appended on the block basis for frame synchronization and word synchronization. The resulting signals are processed with channel coding or translation into signals more amenable to high-density recording, and with data compression. In the recording equalization circuit, the resulting signals are processed with waveforming for correcting the non-linear distortion produced during the recording process. The recording current is supplied to a rotary head via a recording amplifier and a rotary transformer for recording the digital signals on the magnetic tape.
In the reproducing system, the signals read from the magnetic tape are amplified by a playback amplifier and equalized in waveform for producing a waveform with which it is easier to recognize digital signals. From the equalized signals, clocks are reproduced by a PLL circuit by way of clock reproduction for regenerating the recorded digital signals. The synchronizing signals are detected to clarify the points of signal segmentation and the reproduced signals are demodulated and corrected for time-base instability. The signals are corrected and concealed for errors and restored by a digital/analog converter into analog output signals.
If there is only one VTR, the input signals at the input terminal are recorded on a magnetic tape, or the pre-recorded signals are read from the magnetic tape so as to be outputted on a display unit, such as a television receiver. If there are two VTRs connected to each other, it becomes possible to record the signals entered at an input terminal of one of the VTRs or recorded signal on a magnetic tape loaded in the VTR on a magnetic tape loaded on the other VTR, with the signals thus recorded being outputted at an output terminal of the other VTR for being monitored on a display unit.
That is, the digital interfaces of the two VTRs are interconnected and analog signals from a television, a television game unit or an analog VTR are entered to one of the digital VTRs so as to be entered via the digital interfaces to the other digital VTR for recording on the magnetic tape loaded therein, while the signals are simultaneously monitored on a display unit connected to an analog signal output terminal of the other digital VTR. There may be occasions wherein the signals entered in the other digital VTR are the signals read by the firstly stated digital VTR from its magnetic tape.
The color television signals employed in a color television receiver in general, connected to the digital VTR, such as NTSC or PAL system color television signals, are composite color signals composed of luminance signals Y and two chrominance signals R-Y and B-Y, or I signals (broad-range signals) and Q (narrow-range signals) in the case of the NTSC system, multiplexed on the luminance signals by frequency interleaving, and are known as composite signals. On the other hand, Y, R-Y and B-Y or Y, I and Q signals and R, G and B color signals, known as component signals, may be obtained by separating the composite signals into the luminance signals and chrominance signals using a comb-filter by way of Y/C separation, or matrix transformation for R, G and B signals.
The NTSC signals may be generated by capturing the horizontal synchronization signals f.sub.H by a phase-locked oscillator (PLL) for synthesizing color sub-carrier signals f.sub.SC (3.58 MHz), two-phase quadrature modulating the color sub-carrier signals f.sub.SC with the I and Q chrominance signals and by frequency-multiplexing the modulated color sub-carrier signals with the luminance signals Y.
Meanwhile, when the analog video signals entered to one digital VTR or digital video signals reproduced from a magnetic tape of the digital VTR are entered via a digital interface to the other digital VTR, there are occasions wherein the vertical or horizontal synchronizing signals of the input signals are not the standard signals. Consequently, when the input digital video signals are translated into color television signals as output signals, chrominance signals other than standard signals are produced, because the color sub-carrier signals are then produced using the horizontal synchronizing signals which are not standard signals.
For example, output signals of television game sets or analog VTRs may also be entered to the one digital VTR besides the ordinary television signals. Although the usual analog television signals, that is the composite video signals, are outputted from the usual television system, output signals of the television game units or the speed-changed playback signals of the analog VTRs are component signals containing the vertical or horizontal synchronizing signals which are not standard signals contained in the analog television signals. Consequently, if the analog signals are entered via the digital interfaces to the other digital VTR for reproduction subsequently by a television receiver connected to its analog output signal terminal, various inconveniences, such as failure in color display in the displayed image, may be incurred because of the content of the chrominance signals which are not the standard signals.